Technical Field
Devices for and methods of fabrication of three-dimensional objects from powder starting materials.
Description of Related Art
This disclosure relates to a process and apparatus for more efficiently manufacturing three-dimensional (3D) objects from powder materials using a digital fabrication method. The 3D manufacturing process, also known as additive manufacturing, rapid prototyping or solid free form, uses digital files that describe cross sections for building the desired part(s) and support structure(s). Various 3D manufacturing methods have been proposed for digitally fabricating a uniquely shaped object on a build platform. The build rate of digitally produced 3D objects as currently practiced is inherently slow since 1) each 2D layer is typically formed by a two dimensional scanning device and 2) many 2D layers (up to thousands in a high resolution part) are required to produce an object. Furthermore, some manufacturing methods require additional time to post-process a layer before deposition of the next layer. Regardless of the method for building the 3D object, there is a general need to implement process improvements for reducing the time to build uniquely shaped 3D objects.
Various additive manufacturing systems have been proposed to produce three-dimensional objects by either selectively depositing, binding or polymerizing raw materials together in layers. The various alternative methods include filament extrusion techniques, ink jetting, selective laser sintering, powder/binder jetting, electron beam melting, and stereolithographic processes. In general, the various methods tend to exhibit a slow build rate. For example, many of the selective deposition methods have a slow build rate since the deposition of the build and support materials is generally provided by a scanning head for extruding or jetting the material for each layer.
3D manufacturing methods based on electrophotography have been proposed. Although it is recognized that the electrophotographic process can enable formation of 2D layers, researchers have reported problems when attempting to produce arbitrarily thick 3D objects when using conventional electrophotography to produce charged powder depositions that are repeatedly electrostatically transferred and heat fused to the object being built. In one instance, it was found that after about 20 transfers, the object surface had many defects and irregularities that compromised the quality of the object.
In addition to the surface defects problem that arises after many electrostatic transfers of charged powder to build an object, when attempting to build an object using an electrophotographic process, the thickness of the object is self-limited for the conventional electrostatic transfer process. When the electrostatic force for transferring charged powder is provided by an electric field due to an electrical bias applied between the conducting substrate of the build object and the ground plane of the photoconductor, the electric field and correspondingly the applied electrostatic force decreases with increasing thickness of the object. Furthermore, the accumulation of charge on the object due to the charge on the transferred powder creates an electric field that suppresses powder transfer and therefore limits the thickness of the build object and causes irregularities in the surface.
In summary, in currently practiced methods for digitally fabricating 3D objects, the rate for producing 3D objects with such methods is undesirably slow. Accordingly, there remains a need for a high build rate method and apparatus, which can build a three-dimensional part that is free of defects.